Before replacing your PC, some tweaks to try, and benchmark to do.
What hard drive you have, why is it not on UDMA mode 2, what is the transfer rate from the HDD. You may need to unistall the IDE channels in Device Manager, and reboot to let Windows re-install automatically. (see sticky and other posts on enabling DMA in Windows). Use Nero or free program HD Tune to see what transfer rate you get from the HDD. If you have newer HDD with ATA/100-133, you may find a new or used PCI controller for this, so you improve transer rate.
Also do some tests with Nero CD-DVD Speed Test to see how your system is ripping clean pressed DVD-Video, and what numbers you get for burst rate and CPU%. When you run these test, also load Task Manager and monitor CPU%.
My impression you should be able yo safely burn 8X on your system with no other programs running, but I suggest you keep it at 6X anyway.